Guys/Gals,
I'm a new member but have been searching the site for months. I've done a lot of searching but to no avail to my specific problem. I'm very mechanically inclined and 31 years old. Any help is appreciated. Here's my problem:
My car is a 1998 Honda Civic EX with D16Y8 VTEC engine and 5sp MT, 163,000 miles. When the car is cold, I start it up and it has the high idle as it should. However, it stays high and will even top 2000 rpm’s, never coming down. As soon as the car reaches operating temp, I switch the car off and back on immediately and the idle returns to normal, ~760 rpm’s, and runs well the rest of the day. Here are the things I’ve replaced: TPS, IACV, Cap & Rotor, plugs, wires. I’ve cleaned the TB, replaced gaskets, calibrated the new TPS (voltage in range), bled the coolant, adjusted idle per the Service Manual, checked for vacuum leaks, and troubleshooting with multimeter for the past 6 months. Is this a loose wire somewhere? Could the ECT sensor cause this? Could the P2P ECU have a bad circuit? O2 Sensor? I'm at the point of giving up!

 

CEL codes?

 

No sir, not one! Thanks for the reply!

 

CEL work?

If you use your finger to cover the port/hole inside the TB leading to the IACV, does the idle speed drop?

 

The CEL does work. Idle speed drops when hole is covered. I've ordered an OEM throttle body to rule out the aftermarket TPS that I installed and calibrated. If that's not it, that only other thing I can think of is the ECT Sensor or ECU...

 

If you properly calibrated the TPS, I'd cancel the OEM TB and test the ECT sensor.

After installing the new TPS, did you reset the ECU?

 

I've reset the ECU many times as I've been troubleshooting this problem for some time. I'll test the ECT* sensor in the AM and post findings. Thanks for your help, I'm just exhausted fighting this alone and hate posting!

 

It's the 2-wire ECT sensor below the distributor. Measure its resistance after the engine is fully warmed up.

 

Gotcha, this is the one the ECU reads, correct? Should I measure it while car is running and the idle is erratic or switch off to get measurement. I don't have the SM with me now. Thanks!

 

Correct.

Engine and key off. Sensor unplugged.

Should read 200-400 Ohms.

 

Got it, Thanks Ron!

 

I measured 358 on the ECT sensor. I may have found an issue though. While burping the coolant for the 900th time, I had the AC on and I decided to speed up the heat up so the thermostat would release by slightly increasing the RPM's via the throttle wheel. As I did this, I was met with a surging engine, like there was a vacuum leak. Would this mean that the TPS isn't reading the first 5ish% of the throttle advance, thus causing a vacuum leak? I rechecked the TPS and got (.44-4.48). I tried to adjust the throttle wheel screw to get closer to .49 and was met with the surging idle. Thoughts?

 

Don't adjust the TPS voltage with the engine running.

Adjust the TPS voltage to 0.5V with the throttle fully closed, key in ON(II), and the engine off. Then reset the ECU and start the engine to see if the idle speed is improved.

How are you measuring TPS output voltage and adjusting the TPS?

 

That's how I did it exactly. I adjusted the TPS according to a write-up on one of these forums. I set the WOT to 4.5v and tightened the bolts. It called for throttle wheel set screw adjustment for the low side at .49v. By doing this, the screw pushes the throttle open some, causing a leak. If I set the closed throttle setting to .49 via TPS movement, I can't get 4.5v on the high end. I'm measuring TPS voltage with ignition on(II) and reading from the sensor.

 

You are adjusting the TPS backwards. Adjust to 0.5V at closed throttle and then reset the ECU.

Check whether you may have installed the TPS incorrectly. The wheel must be properly aligned with the throttle plate shaft.

 

Ron,
I got up this morning and adjusted the TPS as you stated. Closed Throttle is at .5 and WOT will only show 4.40. After the adjustment and ECU reset, I drove it cold and the problem is still there, but worse. Idle is higher ~2200 rpms and it bucks with the slightest throttle input. This TPS is about 6 months old, would it be bad already or defective? Thanks again man!

 

Remove the TPS to check the installation. The wheel may not be properly aligned with the throttle shaft.

Are you resetting the ECU as described in the Codes sticky at the top?

 

I'll remove the TPS after work to verify. I am confident that it's installed correctly but I'll definately check again. I have been D/C the battery to reset the ECU but will start removing the fuse. I'll report back with findings!

 

To reset the ECU, wait at least 3 minutes before reinstalling the Back Up fuse.

And is not uncommon that the TPS is improperly installed.

 

I'm scared to say I GOT IT, but I believe I've found the problem. I removed the TPS and carefully ensured that the TPS arm was seated between the TB wheel prongs. It was but I removed it anyway for further inspection. What I noticed is that the TPS arm was a lot skinnier than the width of the TB prongs, at least double the width, allowing too much play. I retrieved my trusty pair of needle nose pliers and adjusted the TB prongs to the width of the TPS arm. With a slight snap, the TPS arm was securely back in the TB prongs and I recalibrated. I actually was able to get a .5-4.5v span. After the ECU reset via the backup fuse, I started the car and drove it. No problems at all! The car hasn't had a normal startup in six months until today, so maybe this was the problem. I'll see how it does tomorrow and then I'll feel more confident. Ron, thanks for the walkthrough and helping me track down the problem! I'll post an update in a few days if all is well. Thanks again!

Eric

 

 

So it what the TPS wheel and the TB prongs. I installed last night and didnt connect em. Gonna try this in the morning my civic is hitting 4000rpm. Lol